PPARγ is a member of the nuclear hormone receptor superfamily, and plays an important role in adipocyte differentiation. Hypertrophic adipocytes secrete large amounts of a cytokine such as TNF-α, and free fatty acid which induce insulin resistance. On the other hand, thiazolinedione derivatives such as pioglitazone, rosiglitazone or the like improve insulin resistance by activating PPARγ to decrease hypertrophic adipocytes by apoptosis, and promoting differentiation of preadipocytes into small adipocytes having normal function (J. Biol. Chem., 1995, vol. 270, p. 12953; J. Med. Chem., 1996, vol. 39, p. 665 etc.). Pioglitazone and rosiglitazone, which are PPARγ agonists, have already been clinically used as therapeutic drugs for diabetes (JP-A-61-267580, JP-A-1-131169 etc.).
PPARγ agonists are also useful as agents for treating and/or preventing diseases besides diabetes, such as metabolic syndrome, obesity, impaired glucose tolerance and other insulin resistance syndrome, which are prediabetic conditions, hypertension, atherosclerosis, hyperlipidemia, inflammatory diseases such as psoriasis or the like, inflammatory bowel disease or the like.
On the other hand, angiotensin II receptors increase blood pressure by constricting blood vessels via angiotensin II receptor type 1 on the cellular membrane. Therefore, an angiotensin II receptor antagonist can be an effective agent for treating and/or preventing of cardiovascular diseases such as hypertension or the like (J. Med. Chem., 1996, vol. 39, p. 625). Angiotensin II receptor antagonists such as losartan, candesartan, telmisartan, valsartan, olmesartan or the like have already been used clinically as antihypertensive agents (JP-A-4-364171, JP-A-5-783228 etc.)
It is known that about 60% of hypertensive patients develop complications of impaired glucose tolerance or type 2 diabetes (insulin resistance). Despite the presence of various superior antihypertensive agents, the blood pressure of such patients is poorly managed and positive management of blood glucose is not practiced.
From the foregoing, a drug having a PPARγ agonist activity and an angiotensin II receptor antagonist activity in combination is considered to be useful as an agent for treating and/or preventing diseases related to these two mechanisms, such as type 2 diabetes, impaired glucose tolerance, insulin resistance syndrome, hypertension, hyperlipidemia, metabolic syndrome, visceral obesity, obesity, hypertriglyceridemia, inflammatory dermatic diseases (e.g., psoriasis, atopic dermatitis, seborrheic dermatitis, solar dermatitis etc.), inflammatory diseases (e.g., rheumatoid arthritis, ulcerative colitis, Crohn's disease, endometritis etc.), proliferative diseases (e.g., atherosclerosis, angiostenosis, restenosis etc.), inflammatory neuropsychiatric diseases (e.g., multiple sclerosis etc.), neurodegenerative neuropsychiatric diseases (e.g., Alzheimer's disease, Parkinson's disease etc.), cardiovascular diseases (e.g., arteriosclerosis, cardiac disease, cerebral apoplexy, renal diseases etc.), or the like; particularly type 2 diabetes, impaired glucose tolerance, insulin resistance syndrome, hypertension, hyperlipidemia, metabolic syndrome, visceral obesity, obesity, hypertriglyceridemia, or the like. While an angiotensin II receptor antagonist exhibiting an insulin sensitizing activity has already been reported, the action mechanism thereof has not been clarified (see patent references 1 and 2). In addition, a combination therapy of a thiazolidinedione derivative having a PPARγ agonist activity and an angiotensin II receptor antagonist is known to be effective for the treatment of arteriosclerosis occurring in association with hypertension, obesity associated with diabetes or the like (see patent references 3 and 4). Furthermore, angiotensin II receptor antagonists showing a PPARγ agonist activity have been reported (non-patent reference 1, patent reference 5), and a compound having a PPARγ agonist activity and an angiotensin II receptor antagonist activity in combination is expected to be usable for treating and/or preventing type 2 diabetes, metabolic syndrome and other diseases reactive with a PPARγ agonist, without increasing the risk of fluid accumulation, peripheral edema, lung edema and congestive heart failure, which are induced by PPARγ agonists (patent reference 5).
Meanwhile, a tricyclic compound represented by the following formula (A) and a derivative thereof are known to have an excellent antihypertensive action based on an angiotensin II receptor antagonistic action (see patent references 6 and 9).

In addition, a compound represented by the following formula (B) and a derivative thereof are known as substances suppressing signal transduction of GPR4 (see patent references 7 and 8).
    Patent reference 1: WO 2003/047573    Patent reference 2: WO 2006/107062    Patent reference 3: JP-A-9-323940    Patent reference 4: JP-A-2004-217648    Patent reference 5: WO 2004/014308    Patent reference 6: JP-B-2526005    Patent reference 7: WO 2004/017994    Patent reference 8: WO 2004/017995    Patent reference 9: JP-A-7-61983    Non-patent reference 1: “Hypertension”, 2004, vol. 43, p. 993